The term “electric vehicle” as used herein, includes vehicles having an electric motor for vehicle propulsion, such as battery electric vehicles (BEV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV). A BEV includes an electric motor, wherein the energy source for the motor is a battery that is re-chargeable from an external electric grid. In a BEV, the battery is the source of energy for vehicle propulsion. A HEV includes an internal combustion engine and an electric motor, wherein the energy source for the engine is fuel and the energy source for the motor is a battery. In a HEV, the engine is the main source of energy for vehicle propulsion with the battery providing supplemental energy for vehicle propulsion (the battery buffers fuel energy and recovers kinematic energy in electric form). A PHEV is like a HEV, but the PHEV has a larger capacity battery that is rechargeable from the external electric grid. In a PHEV, the battery is the main source of energy for vehicle propulsion until the battery depletes to a low energy level, at which time the PHEV operates like a HEV for vehicle propulsion.
The electric vehicle monitors the status of the battery using a number of measurements, including battery state of charge (BSOC). BSOC is a percentage that represents the amount of energy in the battery from 0% (empty) to 100% (full). Batteries may be damaged if they are overcharged or overly discharged. Therefore, many prior art electric vehicles maintain the battery within an operating range between a charging limit of approximately 80% BSOC and a discharge limit of approximately 20% BSOC.